Johnny is a sex-crazed fiend who brutalizes elderly women and once broke his brother’s back with a brick.

They are the same man.

The monster accused of raping, beating and robbing a 73-year-old birdwatcher in Central Park suffers from a split-personality disorder that turns him into a completely different person, his brother told The Post yesterday.

“He was diagnosed when he was 14 years old, and it got really bad in his 20s,” said David Albert Mitchell’s brother, Joseph, 42, a chicken farmer who also sells firewood.

“He says that Johnny comes out. I first met Johnny when I was 22 years old. He broke my back. He hit me with a brick. That was the first time I met him, and I never seen him since.

“Guess you all met Johnny out there in New York,” he added.

For years, Johnny was a feared character in Jenkinjones, a tiny, unincorporated township of decrepit houses perched along windy County Road 8.

There are no stores there, only churches.

Every house has a “No Trespassing” sign and every home a gun — a legacy from Mitchell, whose drunken rampages terrorized the townspeople for years.

“He got out of jail, and I told him not to come here because everyone wants to kill him. They’re scared to death of him,” his brother said.

Mitchell’s mom, whom David adored as a boy, also had a split personality.

“She named her Rae,” Joseph recalled. “She was in a wheelchair and very weak, but when Rae came out, she could hop out of her wheelchair.

“But my mother could control it better than David.”

The tight-knit Mitchells were considered the “black sheep of the holler,” he said.

“People didn’t like us, so we moved from house to house. People would burn our houses down, so we would move. We’d go to school and fight; we’d go to the store and fight.”

Shortly before he ended up in New York, Mitchell told his brother that he wanted to see the world.

“He said he never got to see nothing,” Joseph said. “He’s been locked up in prisons his whole life. But I never dreamed he’d make it to New York or do anything up there.”

That Mitchell is in custody, charged with the Central Park rape, is nothing new. He was arrested twice for allegedly raping elderly women in his home state, one of whom was killed, and he was deemed a person of interest in a second murder.

He was acquitted in the rape and murder of Annie Parks, although her nephew said Mitchell was spotted removing bloody sheets from her home.

“He’s always been trouble,” said Claude Johnson.

The list of alleged victims — each older than 50 — includes Virginia James, who barely escaped with her life in 1990 after Mitchell fired a shotgun between her legs after first trying to rape her, her family said.

“He beat up my 80-year-old aunt and tried to rape her. He is an evil man,” Christine Smith, 70, told The Post. “He came in asking for money. She told him she didn’t have any. He beat her. God, did he beat her. There wasn’t a spot on her that wasn’t beaten.

“She was black and blue all over. He pushed her onto her bed. He put a shotgun between her legs and pulled the trigger and fired into the mattress. I don’t know how she got away from him. She ran naked across the yard, across the highway, over a creek and into an apartment building.

“When she got away, he ran. People heard pretty quick what he’d done and went looking for him. They found him at his dad’s house, under the bed, hiding.”

Mitchell was never charged in that attack.

That same year, he brutalized Ruby Dudley, 80, with a fire poker before robbing her, residents said.

Mitchell copped to a plea deal and served eight years for that crime.

“I walked in on him raping her,” recalled Dudley’s nephew, Maurice, who managed to stop the attack 20 years ago.

“He jumped on my aunt. He raped her. I always helped her out and checked on her every day. I knew something was wrong because the door was open. I found him and [her] laying on the floor.”

After Mitchell got out of prison, “everyone was on the lookout,” said Wayne Mitchell (no relation).

“He always broke in on older women,” he said. “I just can’t understand why he was still on the street.